This invention relates to a fuel supply apparatus and, more particularly, to a mounting structure for a fuel supply apparatus for supplying fuel from a fuel tank to a fuel consuming apparatus such as an internal combustion engine.
FIG. 5 is a structural diagram showing the conventional fuel supply apparatus disclosed in Japanese Patent Laid-Open No. 10-31126, for example. FIG. 6 is an enlarged view of a portion A of FIG. 5. In FIGS. 5 and 6, 1 is a fuel tank, 2 is a fuel pump for pumping the fuel to an internal combustion engine, and 3 is a set plate made of a synthetic resin for supporting the fuel pump 2 and the like. The set plate 3 is provided to close an opening hole 1a disposed in the top surface of the fuel tank 1 with a gasket 5 made of synthetic rubber for maintaining a seal between the fuel tank 1 and the set plate 3 interposed therebetween, and the set plate 3 is secured thereto by tightening bolts 7 to fasten a holding plate 4 which holds an outer peripheral portion of the set plate 3 to the top of the fuel tank 1.
The material used commonly in forming the set plate 3 is polyacetal resin, or polyoxymethylene (hereinafter referred to as POM) resin. The material used commonly in forming the plate 4 is iron sheet or iron sheet plated with zinc.
In such the conventional mounting structure for the fuel supply apparatus, the set plate 3 made of POM resin and the plate 4 made of iron or iron plated with zinc are in direct contact with each other. The fuel tank 1 is generally mounted under the floor of an automobile body, so that the plate 4 exposed outside of the fuel tank is exposed to salt sprayed for thawing snow during winter in cold districts and to salt particles in sea wind in coastal areas. Under these environmental circumstances, chemical reactions that could take place on the surface of the plate 4 will be explained in conjunction with reaction formulae (1) to (8) given below.
xe2x80x83Fe+CaCl2xe2x86x92FeCl2+Caxe2x80x83xe2x80x83formula (1)
Zn+CaCl2xe2x86x92ZnCl2+Caxe2x80x83xe2x80x83formula (2)
Fe+2NaClxe2x86x92FeCl2+2Naxe2x80x83xe2x80x83formula (3)
Zn+2NaClxe2x86x92ZnCl2+2Naxe2x80x83xe2x80x83formula (4)
FeCl2+H2Oxe2x86x92HCl+Fe.(OH)(Cl)xe2x80x83xe2x80x83formula (5)
ZnCl2+H2Oxe2x86x92HCl+Zn.(OH)(Cl)xe2x80x83xe2x80x83formula (6)
HClxe2x86x92H++Clxe2x88x92xe2x80x83xe2x80x83formula (7)
xe2x80x94(CH2xe2x80x94O)xe2x80x94nH+xe2x86x92decomposes to monomerxe2x80x83xe2x80x83formula (8)
On the surface of the plate 4 made of iron or zinc-plated iron, iron oxide or zinc chloride would be generated as a result of a chemical reaction with calcium chloride in salt for thawing snow or with sodium chloride in seawater as shown in reaction formulae (1) to (4).
In addition, iron oxide or zinc chloride thus generated reacts with water as shown in reaction formulae (5) or (6) and generates hydrochloric acid. When hydrochloric acid deposits on the set plate 3 made of POM resin, the Cxe2x80x94O bond cleavage would take place in the POM resin due to the presence of the acid (H+) as shown in reaction formulae (7) and (8), leading to decomposition of the resin. Thus, the set plate 3 has a problem of potential surface corrosion or deterioration.
This invention has been made to resolve the problem described above, and has as its object the provision of a fuel supply apparatus mounting structure in which the set plate for fitting a fuel supply apparatus is free from the problem of corrosion or deterioration.
The present invention resides in a mounting structure for a fuel supplying apparatus for mounting a fuel pump, which pumps fuel to an internal combustion engine, to an opening hole in a fuel tank to close the opening hole, comprising, a set plate made of a synthetic resin for supporting the fuel pump and placed over the opening hole in the fuel tank, a gasket disposed between the set plate and the fuel tank, and a gasket disposed between the set plate and the plate for maintaining a fluid tight relationship therebetween and the structure is characterized in that a protective member, which is made of a material that is not reacted, dissolved or deteriorated by a reaction product generated by a chemical reaction between the plate and the set plate, is inserted between the plate and the set plate. The plate may be made of an iron sheet or zinc plated iron sheet and said set plate may be made of polyacetal resin. The protective member may be formed as an integral, one-piece structure with said gasket, a coating layer formed on said plate, a synthetic rubber or epoxy resin.